1. FIELD OF THE INVENTION
This invention relates to contact metallization on silicon carbide, specifically, to Schottky contacts of platinum and platinum silicide on B-silicon carbide.
2. DESCRIPTION OF THE PRIOR ART
The excellent electrical characteristics coupled with the superior thermal properties of silicon carbide (SiC) make it a viable semiconductor for high temperature, high frequency and high power device applications, such as IMPATTs and power FETs. Its high electron mobility and large saturated drift velocity (2.times.10.sup.17 cm/sec) make SiC useful for high frequency electronic device applications. In addition, its wide band-gap, chemical inertness and refractory nature make SiC a viable material for high temperature, high reliability microwave devices.
Silicon carbide comes in more than hexagonal and rhombohedral polytypes, known as .alpha.-SiC, and one zinc-blend cubic polytype, referred to as .beta.-SiC, which is characterized by higher electron mobility, especially at elevated temperatures, and a smaller energy gap than .alpha.-SiC. Also, .beta.-SiC can be grown on Si substrates at relatively low temperatures. For these reasons, the .beta.-SiC is preferred for microelectronic applications.
In order to realize device structures such as MESFETs, IMPATTs and photodiodes on SiC, both rectifying Schottky and ohmic contact metallizations must exist. The refractory features of SiC become useful only when they are combined with thermally stable and reliable contacts High temperature applications of SiC devices will be essentially limited by the metal-SiC contact characteristics. Devices made with SiC are expected to be operated at temperatures exceeding 600.degree. C. either because of high temperature environments or because of high power requirements where heat dissipation causes self-heating of the device active regions.
Investigations of Schottky-barrier contacts on .alpha.-SiC involving Au and Ag ("Surface-Barrier Diodes on Silicon Carbide", S. H. Hagen, J. of Appl. Phys. Vol. 30, No. 3, p. 1458 15 Feb. 1968; Au-SiC Schottky Diodes, S. Y. Wu and R. B. Campbell, Solid-State Electronics, Vol. 17, p 683, 1974), showed these metallizations were independent of the work function of the metal studied or the SiC polytype used. Work on chromium Schottky contacts on various .alpha.-SiC polytypes ("Influence of Vacancies on the Formation of Surface Barriers in SiC Polytypes", Soviet Physics Semiconductors, Vol. 17(10), Oct. 1983) revealed a dependence of the barrier height on the degree of hexagonality of the SiC.
The first investigation of Schottky barriers on .beta.-SiC was performed by Yoshida et al. as reported in "Schottky Barrier Diodes on 3C-SiC", Applied Physics Letters, Vol. 46(8), 15 Apr. 1985. Au is the only metal that has been shown to produce wellbehaved rectifying contact on SiC. A subsequent study ("The Effect of Heat Treatment on Au Schottky Contacts on .beta.-SiC", D. E. Ioannou, N. A. Papanicolaou, P. E. Nordquist, IEEE Transactions on Electron Devices, Vol. ED-34(8), Aug. 1987) of thermally treated Au Schottky contacts on .beta.-SiC showed that the rectifying characteristics of these diodes degrade at temperatures as low as 350.degree. C. Another problem associated with Au contacts is the poor adhesion of the metal to the SiC which makes the contacts susceptible to scratching and peeling during processing and probing. There is a need for the development of thermally stab)e and rugged contact metallization schemes on .beta.-SiC.